ISO 4628-2:2016

Overview

ISO 4628-2:2016 - Paints and varnishes: Evaluation of degradation of coatings - Part 2: Assessment of degree of blistering - specifies a visual method for rating blistering in coatings by comparison with pictorial standards. The standard provides calibrated images for blister sizes S2–S5 and quantity (density) ratings 2–5, defines how to express results (for example 2(S2)), and sets requirements for illumination and reporting. It supports consistent, reproducible assessment of coating degradation such as blisters caused by ageing, weathering or substrate issues.

Key topics and requirements

• Pictorial standards: Illustrative plates for blisters of sizes S2, S3, S4 and S5, each shown at densities 2–5 for direct comparison during assessment.
• Designation system: Uses the ISO 4628 series convention to report quantity (density) and size, e.g. “degree of blistering 2(S2)”.
• Assessment conditions:
  • Perform visual assessment under good illumination as specified by ISO 13076 (lighting and procedure for visual assessments).
  • Note: S1 blisters are generally not visible without ×10 magnification.
• Optical imaging: If using cameras or automated imaging systems, calibrate the system using the calibration images in Annex A.
• Reporting requirements: Test report should include coating identification, reference to ISO 4628-2, surface type and area, result (rating and percentage of area affected), illumination used, anomalies, and date of examination.
• Correlation: Annex B provides a correlation between ISO 4628-2 and ASTM D714 blister rating systems for cross-standard interpretation.

Practical applications

• Quality control and acceptance testing for painted and varnished surfaces in manufacturing and construction.
• Field and laboratory inspections for corrosion protection, maintenance planning, failure analysis, and warranty investigations.
• Specification and contract language for coating performance, enabling objective pass/fail criteria.
• Useful for OEMs, coating formulators, inspectors, corrosion engineers, maintenance managers, and testing laboratories who require standardized, comparable assessments of blistering.

Related standards

• ISO 4628-1 - General introduction and designation system (essential for interpreting ratings).
• ISO 13076 - Lighting and procedure for visual assessments (illumination requirements).
• ASTM D714 - US standard for evaluating degree of blistering (see Annex B correlation).

Keywords: ISO 4628-2:2016, blistering, coatings assessment, paints and varnishes, pictorial standards, calibration images, ISO 13076, ASTM D714, coating degradation, visual inspection.